The present invention relates, according to an aspect thereof, to an arrangement for supplying oil to a brake.
The invention, according to an aspect thereof, is applicable on working machines within the fields of industrial construction machines in particular wheel loaders. Although aspects of the invention will be described hereinafter with respect to a wheel loader, the invention is not restricted to this particular machine, but may also be used in other heavy working machines, such as articulated haulers, dump trucks, graders, excavators or other construction equipment.
Working machines, such as articulated haulers, wheel loaders, motor graders, excavators and other construction equipments are often equipped with wet disc brakes in order to provide a sufficient brake capacity and long service intervals. A wet disc brake uses a cooling liquid, usually some kind of oil or oil emulsion, to cool the brake discs in the disc brake. The cooling liquid is provided in a compartment where the brake is mounted, usually in the wheel hubs of the vehicle. The hub is filled with oil such that at least parts of the brake discs are submerged in the oil. The oil is thus in contact with the brake discs and the brake liners and is used to cool the brake, since oil has a better heat conductivity that air, especially in an enclosed brake arrangement.
In order to improve the brake capacity and to prevent brake fading, it is known to use an oil pump to actively supply the brake with oil instead of just letting the brake discs be immersed in the oil. An oil pump will improve the oil flow through the disc brake, which in turn will improve the cooling capacity of the oil. The oil will take up the heat from the brake and will distribute the heat to the larger part of the wheel hub where the brake is positioned. The cooling surface for the oil is thus enlarged. The brake capacity may be improved further by increasing the oil volume and/or the cooling of the oil. This can be done by using an external oil reservoir and/or an external oil cooler.
Such heavy vehicles are often provided with a hub reduction gear in order to improve the driving torque of the vehicle while at the same time reducing the stress put on the drive train and the differential of the vehicle. The hub reduction is normally a planetary gear which reduces the rotational speed from the incoming drive shaft and at the same time raises the driving torque with the same factor. The wet disc brake is mounted in the wheel hub. It is possible to mount the wet disc brake in two different positions in the wheel hub, either before or after the planetary gear.
If the wet disc brake is mounted before the planetary gear, it will rotate with the speed of the drive shaft which rotates with a relatively high rotational speed. The required brake torque is relatively low. The generated heat will heat the brake oil which must be cooled. If self-circulation is not enough, it is possible to use an external oil pump to increase the oil flow through the wet disc brake. Since the rotational speed of the drive shaft and thus of the brake discs is relatively high, it is possible to mount the oil pump with the brake discs in order to drive the oil pump. The high rotational speed of the oil pump will secure an oil flow through the wet disc brake.
A wet disc brake mounted after the planetary gear will rotate with the same speed as the wheel, which rotates with a relatively low rotational speed. The required brake torque will be relatively high. The generated heat will be approximately the same. If self-circulation is not enough to cool the brake oil, it is possible to use an external oil pump to increase the oil flow through the wet disc brake. Due to the low rotational speed of the wheel and thus of the brake, it is not possible to mount the oil pump with the brake since the oil flow from an oil pump rotating with such a low rotational speed will not be enough to pump a sufficient amount of oil through the wet disc brake. This is especially the case for centrifugal pumps that will not function properly at low rotational speeds. For a wet disc brake rotating with the wheel speed, it is thus necessary to use an external oil pump driven by an external power source, either a mechanical power outlet or an electric motor.
JP 55107132 A describes a reduction hub of a vehicle having a vane portion which functions as an oil pump for circulating oil through a wet disc brake. The created oil pump rotates with the same speed as the wheels of the vehicle.
The system described in JP 55107132 A and other known systems operate satisfactorily for some applications. There is however still room for improvements.
It is desirable to provide an improved oil supply arrangement for a brake in a vehicle. It is also desirable to provide an oil supply arrangement having an improved cooling capacity.
In an arrangement for supplying oil to a brake arranged for braking an output shaft of a planetary gear, where the arrangement comprises a rotatable impeller for supplying oil to the brake, the impeller is arranged to be rotated by an input shaft of the planetary gear.
By this first embodiment of the oil supply arrangement according, to an aspect of the invention, an oil pump that rotates with a high rotational speed and that can supply oil to a brake that rotates with a lower rotational speed is obtained. In this way, the impeller of the oil pump is mounted before the planetary gear such that it rotates with the speed of the input axle and the brake is mounted after the planetary gear such that it rotates with a lower speed. In this way, the oil pump can supply oil to the brake without the need of an external power source. This allows for a simple and cost-effective solution having few additional parts.
In an advantageous development of the inventive oil supply arrangement, the impeller is mounted on or to the sun gear of the planetary gear. In this way, the impeller will rotate with the speed of the input shaft which may be either a drive shaft for a wheel or a propeller shaft mounted before a differential. In either case, the impeller will rotate with a relatively high speed. Since the speed of the input shaft will be dependent on the travelling speed of the vehicle, the oil pump will be able to supply a substantial amount of oil when the vehicle is moving, i.e. when there is a need to cool the brake of the vehicle. The amount of supplied oil will also depend on the reduction ratio of the planetary reduction gear.
In a further advantageous development of the inventive oil supply arrangement, the oil pump comprises at least one oil conduit adapted to feed oil directly to the brake. In this way, the oil can be directed and distributed to parts of the brake where the cooling is most favourable. By including an oil distributor to the oil conduit, the oil can be distributed e.g. to separate brake discs and to separate brake linings of the brake. In this way, it is guaranteed that all brake discs are supplied with oil and that no brake disc is overheated due to an uneven oil distribution.
In a further advantageous development of the inventive oil supply arrangement, the brake is a wet disc brake. Disc brakes are well suited for the cooling with oil and can deliver a high and reliable brake torque. A wet disc brake is also well suited to be enclosed inside a wheel hub or a rear axle.
In a further advantageous development of the inventive oil supply arrangement, the arrangement is mounted in an axle casing having one or more oil channels for transporting the heated oil from the brake to a remote inner part of the axle. In this way, the axle casing can help to cool the oil due to a larger contact surface for the oil. Further, the cooling of the oil is aided due to the fact that the oil is distributed over a larger surface inside the axle. When the brake is mounted in the wheel hub of a vehicle, it is also possible to mix the oil of two adjacent wheel hubs, which may be of advantage if the brake on one side of the vehicle is used more than the other.